1. Field of the Invention
The present invention relates to a three-leg power converter apparatus, and more particularly to a power converter apparatus with three input/output ports for converting electrical power between these three ports.
2. Description of the Related Art
Recently, owing to the rapid development in Power Electronics, some apparatuses based on technology of power electronics have been applied to fields relative to power conversion. Basically, there are four typical types in operation of power conversion: AC/DC, DC/DC, DC/AC, and AC/AC, which are realized by apparatuses such as AC/DC converters, DC/DC converters, DC/AC inverters and AC/AC converters. Generally, a power converter apparatus with single power stage can only complete one of said typical types in operation of power conversion, and plural and different types of power converters are required while a complex power conversion function has to be achieved.
For example, a conventional on-line UPS (uninterruptible power supply) system shown in FIG. 1 includes two power stages 91, 92, wherein the power stage 91 is an AC/DC converter and the other power stage 92 is a DC/AC inverter, so that a normal AC power can be converted into an AC power for an AC load. Furthermore, a conventional off-line UPS system with small capacity is illustrated in FIG. 2. Regarding to the off-line UPS system, a requirement for providing two power stages 93, 94 is needed because the battery voltage of a limited amount of batteries is evidently lower than the required DC voltage of DC/AC inverter 94 applied in the off-line UPS system. The power stage 93 is a DC/DC converter acting as a boost converter for raising a DC voltage of the batteries, and the power stage 94 is a DC/AC inverter for converting the DC power generated by the power stage 93 into an AC power for an AC load. Moreover, a kind of power converter apparatuses for a photovoltaic generation system disclosed in US patents numbered U.S. Pat. No. 7,079,406 and U.S. Pat. No. 6,678,174 is illustrated by FIG. 3. In the above-mentioned power converter apparatus, there are two power stages 95, 96 connected between a solar cell array and an AC power distribution system, with the power stage 95 converting a variable DC power generated by the solar cell array into a regulated DC power and the power stage 96 further converting the DC power into an AC power and then injecting the AC power into the AC power distribution system.
Accordingly, for most conventional power converter apparatuses to complete a complex power conversion operation including at least two typical types in operation of power conversion, at least two power stages are required. Hence, the power electronic circuits and the control circuits of conventional power converter apparatuses with complex power conversion operation are complicated, and a cost for manufacture of the conventional power converter apparatus is high. As a result, there is a need for redesigning the conventional power converter apparatus for implementation thereof.